U.S. patent application number 10/979446 was filed with the patent office on 2005-05-12 for membrane electrode assembly, manufacturing process therefor and direct type fuel cell therewith.
Invention is credited to Mizukoshi, Takashi, Nishiyama, Toshihiko, Shimizu, Kunihiko.
Application Number | 20050100778 10/979446 |
Document ID | / |
Family ID | 34544605 |
Filed Date | 2005-05-12 |
United States Patent
Application |
20050100778 |
Kind Code |
A1 |
Shimizu, Kunihiko ; et
al. |
May 12, 2005 |
Membrane electrode assembly, manufacturing process therefor and
direct type fuel cell therewith
Abstract
This invention relates to a membrane electrode assembly
comprising a fuel electrode, an air electrode and an electrolyte
membrane where micropores in a porous membrane is filled with a
proton conducting polymer, wherein on at least one side of the
electrolyte membrane is formed a planarizing layer, via which a
fuel electrode or air electrode is formed, as well as a direct type
fuel cell therewith.
Inventors: |
Shimizu, Kunihiko; (Miyagi,
JP) ; Nishiyama, Toshihiko; (Miyagi, JP) ;
Mizukoshi, Takashi; (Miyagi, JP) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
34544605 |
Appl. No.: |
10/979446 |
Filed: |
November 2, 2004 |
Current U.S.
Class: |
429/483 ;
429/490; 429/494; 429/535; 502/101 |
Current CPC
Class: |
H01M 8/106 20130101;
Y02E 60/50 20130101; Y02P 70/50 20151101; H01M 8/1011 20130101;
H01M 8/1053 20130101; H01M 4/8605 20130101; H01M 8/1004 20130101;
H01M 8/0289 20130101; H01M 8/1072 20130101 |
Class at
Publication: |
429/040 ;
429/044; 429/042; 502/101; 429/030 |
International
Class: |
H01M 004/86; H01M
004/96; H01M 004/88; H01M 008/10 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 11, 2003 |
JP |
2003-380606 |
Claims
What is claimed is:
1. A membrane electrode assembly comprising a fuel electrode, an
air electrode and an electrolyte membrane where micropores in a
porous membrane is filled with a proton conducting polymer, wherein
on at least one side of the electrolyte membrane is formed a
planarizing layer, via which a fuel electrode or air electrode is
formed.
2. The membrane electrode assembly as claimed in claim 1, wherein
in the air electrode side of the electrolyte membrane is formed a
hydrophobic film as the planarizing layer, via which an air
electrode is formed.
3. The membrane electrode assembly as claimed in claim 1, wherein
in the fuel electrode side of the electrolyte membrane is formed a
hydrophilic film as the planarizing layer, via which a fuel
electrode is formed.
4. The membrane electrode assembly as claimed in claim 1, wherein
in the air electrode side of the electrolyte membrane is formed a
hydrophobic film as the planarizing layer, via which an air
electrode is formed, while in the fuel electrode side of the
electrolyte membrane is formed a hydrophilic film as the
planarizing layer, via which a fuel electrode is formed.
5. The membrane electrode assembly as claimed in claim 2, wherein
the hydrophobic film is made of a hydrophobic organic material or a
hydrophobic material comprising a composite of a carbon material
and a hydrophobic organic material.
6. The membrane electrode assembly as claimed in claim 3, wherein
the hydrophilic film is made of a hydrophilic material comprising
an organic material having an ionic group.
7. The membrane electrode assembly as claimed in claim 1, wherein
the porous membrane is made of a polymer material.
8. The membrane electrode assembly as claimed in claim 1, wherein
the porous membrane is made of a material selected from a
polyimide, a perfluorocarbon polymer and a polyolefin.
9. A process for manufacturing the membrane electrode assembly as
claimed in any of claims 1 to 8, comprising the steps of: forming
the electrolyte membrane by introducing a polymerizable material
comprising a monomer having a sulfonic acid group into micropores
in the porous membrane for initiating a reaction of the monomer to
form the proton conducting polymer for filling the micropores in
the porous membrane; and forming a planarizing layer on at least
one side of the electrolyte membrane.
10. The process for manufacturing a membrane electrode assembly as
claimed in claim 9, wherein the monomer having a sulfonic acid
group is an acrylic monomer or olefinic monomer having a sulfonic
acid group.
11. The process for manufacturing a membrane electrode assembly as
claimed in claim 9, wherein a hydrophobic planarizing layer is
formed by applying a hydrophobic organic material or a hydrophobic
material comprising a composite of a carbon material and a
hydrophobic organic material to the air electrode side of the
electrolyte membrane.
12. The process for manufacturing a membrane electrode assembly as
claimed in claim 9, wherein a hydrophilic planarizing layer is
formed by applying a hydrophilic material comprising an organic
material having an ionic group to the fuel electrode side of the
electrolyte membrane.
13. A direct type fuel cell comprising the membrane electrode
assembly as claimed in any of claims 1 to 8.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a fuel cell, in particular to a
membrane electrode assembly, a manufacturing process therefor and a
direct type fuel cell therewith.
[0003] 2. Description of the Related Art
[0004] FIG. 2 is a schematic cross-sectional view of a membrane
electrode assembly (MEA) used in a conventional wet direct type
fuel cell. In this figure, 1 is an alcohol fuel, 2 is a
fuel-electrode side catalyst layer, 4 is a porous polymer membrane,
5 is a part filled with a proton conducting polymer, and 7 is an
air-electrode side catalyst layer. A wet direct type fuel cell
comprising such a membrane electrode assembly (MEA) as a unit has
properties suitable as a small and portable fuel cell.
[0005] It is well-known that in a wet type ion-conducting polymer
electrolyte membrane generally operated in a fuel cell at a
temperature of 100.degree. C. or less, proton conductivity becomes
higher as the number of an anionic group such as a sulfonic acid
group is increased in the polymer side chain.
[0006] However, a polymer electrolyte membrane having an ionic
group in its side chain has a drawback that since the ionic group
is also hydrophilic, an increased number of such ionic groups may
lead to a more hydrated polymer electrolyte membrane, whose volume
tends to be varied due to swelling, resulting in a weaker polymer
electrolyte membrane.
[0007] There is also a problem that swelling of a polymer
electrolyte membrane with water may increase proton transferring
paths to improve proton conductivity while allowing an alcohol as a
fuel to more easily penetrate the electrolyte membrane. The problem
is called "crossover", where a fuel penetrates an electrolyte
membrane and reacts with an air electrode, i.e., a chemical
short-circuit reaction, leading to reduction in a battery
output.
[0008] These problems may be solved by use a thicker electrolyte
membrane for reducing penetration by an alcohol to ensure a
mechanical strength. It, however, leads to increase in an
electrolyte membrane resistance.
[0009] There has been disclosed a method for ensuring a mechanical
strength of an electrolyte membrane by adding a non-proton
conductive reinforcing material represented by
polytetrafluoroethylene (hereinafter, referred to as "PTFE") or
crosslinking electrolyte polymers. For example, JP-H06-275301-A has
disclosed a solid polymer electrolyte type fuel cell comprising an
ion exchange membrane consisting of a cross-linked perfluorocarbon
polymer having a sulfonic acid group.
[0010] These methods, however, also have a drawback that mobility
of protons is reduced, resulting in increase in an specific
resistance of an electrolyte membrane per a unit thickness even
when a thickness of the electrolyte membrane can be reduced.
[0011] To solve the above problem, there has been disclosed an
electrolyte membrane wherein a proton conductive material is filled
in an non-proton conductive porous membrane having good mechanical
strength. Mechanical strength can be ensured by the porous polymer
membrane as a base and proton conductivity can be ensured by the
proton conductive material filled within micropores in the porous
membrane. In such an electrolyte membrane, the number of a sulfonic
acid group can be increased to improve proton conductivity because
mechanical strength is not required to the proton conductive
material. For example, JP-2003-263998-A has disclosed an
electrolyte wherein a proton conducting polymer having an
ion-exchange group such as --SO.sup.3-- is filled in micropores in
a porous base made of a polyimide or polyamide.
[0012] In the electrolyte membrane where a proton conductive
material is filled in micropores in a porous polymer membrane
having good mechanical strength, swelling with water is reduced so
that a three dimensional structure of the polymer can be controlled
to prevent an alcohol from penetrating. That is, crossover can be
prevented, allowing a high concentration fuel to be employed.
[0013] Such a polymer electrolyte where a proton conductive
material is filled in micropores in a porous membrane is a
composite material. In an electrolyte membrane made of such a
composite material, it is difficult to control the conditions such
that the surface of the electrolyte membrane becomes flat while the
proton conductive material is filled. Thus, there is a problem that
its contact in an interface with a catalyst electrode layer is
inadequate, often resulting in increase in a contact
resistance.
[0014] JP-2001-294705-A has described that a porous membrane made
of an aliphatic hydrocarbon polymer such as a polyolefin resin can
be sulfonated in a vapor phase and then fused for closing holes to
provide an electrolyte membrane. The membrane, however, does not
exhibit satisfactory properties.
[0015] A direct type fuel cell can directly use a liquid fuel with
a higher energy density in a fuel electrode. In contrast, a space
for the use of a gaseous fuel or a reformer is needed in a gaseous
fuel type fuel cell using a gaseous fuel including compressed gas
or a reforming type fuel cell using a gaseous fuel made from the
liquid fuel. A direct type fuel cell has been, therefore, being
intensely studied because it can be made more compact than any of
these types of fuel cells and is suitable for a small and portable
fuel cell.
[0016] In a direct type fuel cell using a liquid as a fuel, a fuel
electrode side is contiguous to a liquid phase while an air
electrode side is contiguous to a gaseous phase. In the air
electrode side, water generated by a chemical reaction during
electric power generation and moving water penetrating an
electrolyte membrane tend to prevent oxygen from moving in a
gaseous phase in a diffusion layer in an air electrode. When the
phenomenon is significant, it may cause reduction in a battery
output, so-called "flooding". To avoid the problem, it is desirable
to make the air electrode side water-repellant for preventing
moisture from becoming droplets to avoid interference with oxygen
transfer.
[0017] On the other hand, the fuel electrode side contiguous to a
liquid phase is desirably hydrophilic for promoting movement of an
aqueous alcohol solution as a fuel, which then reacts with a
fuel-electrode catalyst electrode to generate protons, and
promoting transfer of the protons generated to an electrolyte
membrane. Particularly, when a large current is discharged, i. e.,
when a large number of protons move, a more sufficiently
hydrophilic environment is desired. In such a case, it is known
that proton transfer is promoted when a catalyst layer is in close
contact with an electrolyte membrane.
[0018] In the prior art, the above problems have been dealt by
adding a hydrophilic or hydrophobic material to a catalyst
electrode side, but it is not adequately effective.
SUMMARY OF THE INVENTION
[0019] An objective of this invention is to provide a membrane
electrode assembly comprising an electrolyte membrane having both
excellent proton conductivity and excellent mechanical strength as
well as good adhesiveness to a catalyst electrode layer, whereby a
battery output can be improved, and a direct type fuel cell
therewith.
[0020] According to an aspect of this invention, there is provided
a membrane electrode assembly comprising a fuel electrode, an air
electrode and an electrolyte membrane where micropores in a porous
membrane is filled with a proton conducting polymer, wherein on at
least one side of the electrolyte membrane is formed a planarizing
layer, via which a fuel electrode or air electrode is formed.
[0021] In the membrane electrode assembly of this invention, in the
air electrode side of the electrolyte membrane may be formed a
hydrophobic membrane as the planarizing layer, via which an air
electrode is formed.
[0022] In the membrane electrode assembly of this invention, in the
fuel electrode side of the electrolyte membrane may be formed a
hydrophilic membrane as the planarizing layer, via which a fuel
electrode is formed.
[0023] In the membrane electrode assembly of this invention, in the
air electrode side of the electrolyte membrane may be formed a
hydrophobic film as the planarizing layer, via which an air
electrode is formed, while in the fuel electrode side of the
electrolyte membrane may be formed a hydrophilic film as the
planarizing layer, via which a fuel electrode is formed.
[0024] In the membrane electrode assembly of this invention, it is
preferable that the hydrophobic film is made of a hydrophobic
organic material or a hydrophobic material comprising a composite
of a carbon material and a hydrophobic organic material, and that
the hydrophilic film is made of a hydrophilic material comprising
an organic material having an ionic group.
[0025] In the membrane electrode assembly of this invention, the
porous membrane is preferably made of a polymer material.
[0026] In the membrane electrode assembly of this invention, the
porous membrane is preferably made of a material selected from a
polyimide, a perfluorocarbon polymer and a polyolefin.
[0027] According to another aspect of this invention, there is
provided a process for manufacturing the membrane electrode
assembly described above, comprising the steps of forming the
electrolyte membrane by introducing a polymerizable material
comprising a monomer having a sulfonic acid group into micropores
in the porous membrane for initiating a reaction of the monomer to
form the proton conducting polymer for filling the micropores in
the porous membrane; and forming a planarizing layer on at least
one side of the electrolyte membrane.
[0028] In the process for manufacturing a membrane electrode
assembly according to this invention, the monomer having a sulfonic
acid group is preferably an acrylic monomer or olefinic monomer
having a sulfonic acid group.
[0029] In the process for manufacturing a membrane electrode
assembly according to this invention, a hydrophobic planarizing
layer may be formed by applying a hydrophobic organic material or a
hydrophobic material comprising a composite of a carbon material
and a hydrophobic organic material to the air electrode side of the
electrolyte membrane.
[0030] In the process for manufacturing a membrane electrode
assembly according to this invention, a hydrophilic planarizing
layer may be formed by applying a hydrophilic material comprising
an organic material having an ionic group to the fuel electrode
side of the electrolyte membrane.
[0031] According to another aspect of this invention, there is
provided a direct type fuel cell comprising a membrane electrode
assembly of this invention.
[0032] In this invention, a planarizing layer is formed on the
surface of an electrolyte membrane in which a proton conducting
polymer is filled in micropores in a porous membrane so that a
membrane surface can be planarized to improve adhesiveness of a
catalyst electrode layer to the electrolyte membrane. Application
of a hydrophobic material to the membrane surface in the air
electrode side can prevent penetration of water or droplet forming
from water generated so that oxygen can be smoothly transferred.
Furthermore, application of a hydrophilic material to the membrane
surface in the fuel electrode side can improve ion conductivity.
Owing to these effects, a direct type fuel cell with an improved
output can be provided.
[0033] In other words, according to this invention, an electrolyte
membrane in which micropores in a porous membrane are filled with a
proton conducting polymer is used and a planarizing layer is formed
between the electrolyte membrane and a catalyst electrode layer to
improve adhesiveness between them. Thus, there can be provided a
membrane electrode assembly having both adequate proton
conductivity and adequate mechanical strength which allows a
battery output to be improved, and a direct type fuel cell
therewith. Furthermore, a hydrophilic film as a planarizing layer
formed in a fuel electrode side can improve proton conductivity
while a hydrophobic film as a planarizing layer formed in an air
electrode can prevent flooding, allowing a battery output to be
further improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic cross-sectional view of a membrane
electrode assembly according to this invention.
[0035] FIG. 2 is a schematic cross-sectional view of a membrane
electrode assembly according to the prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] There will be described the most preferred embodiments of
this invention with reference to the structure of a membrane
electrode assembly (MEA) according to this invention illustrated in
the drawing. FIG. 1 is a schematic cross-sectional view of a
membrane electrode assembly (MEA) according to this invention. In
this figure, 1 is an alcohol fuel, 2 is a fuel-electrode side
catalyst layer, 3 is a hydrophilic material layer, 4 is a porous
polymer membrane, 5 is a part filled with a proton conducting
polymer, 6 is a hydrophobic material layer and 7 is an
air-electrode side catalyst layer.
[0037] The MEA comprises, as an electrolyte membrane, a porous
membrane filled with a proton conducting polymer. The sides of the
electrolyte membrane comprise a hydrophilic material layer 3 and a
hydrophobic material layer 6, respectively. Furthermore, a
fuel-electrode side catalyst layer 2 (fuel electrode) and an
air-electrode side catalyst layer (air electrode) are formed via
the hydrophilic material layer 3 and the hydrophobic material layer
6, respectively.
[0038] A suitable porous membrane is a porous polymer membrane; for
example, a porous membrane made of a nonionic polymer material
including perfluorocarbon polymers such as polytetrafluoroethylene
(PTFE), polyimides and polyolefins such as polyethylene. If
necessary, these polymer materials can be used after
hydrophilization by, for example, introducing a hydrophilic group.
Among these, a porous membrane made of a perfluorocarbon polymer,
particularly a hydrophilized PTFE porous membrane can be suitably
used, but there are no particular restrictions to a material, a
film thickness, porosity, hydrophilicity or hydrophobicity as long
as a desired electrolyte membrane can be provided.
[0039] A proton conducting polymer filled in micropores in a porous
membrane may be a polymer electrolyte having an ion exchange group
such as a sulfonic acid group containing a proton which is readily
released; for example, an acrylic or polyolefinic polymer
electrolyte having an ion exchange group in its side chain.
[0040] A proton conducting polymer can be filled in micropores in a
porous membrane by, for example, impregnating the porous membrane
with a raw material solution containing a monomer having an ion
exchange group and polymerizing the monomer as described below.
Examples of a suitable monomer having an ion exchange group include
an acrylic monomer having a sulfonic acid group and an olefinic
monomer having a sulfonic acid group.
[0041] A raw material solution for producing a proton conducting
polymer may consist of a monomer, a solvent and a radical
polymerization initiator. The raw material solution may further
contain a crosslinking agent and an additional copolymerizable
monomer.
[0042] A porous membrane is impregnated with the raw material
solution, which is then polymerized and dried. Then, the membrane
is soaked in a washing liquid to remove unpolymerized materials and
low-polymerized products. If necessary, the above process of
impregnation and polymerization can be repeated, depending on a
thickness and a porosity of the porous membrane and a filling rate
of the proton conducting polymer.
[0043] On one side of the electrolyte membrane is applied a
hydrophobic material to form a hydrophobic material layer in the
air electrode side. A suitable hydrophobic material is a
hydrophobic organic material, particularly a nonionic polymer
compound. For example, a perfluorocarbon polymer such as PTFE can
be used. The hydrophobic material may further contain a carbon
material such as Ketjen Black and carbon black. As long as desired
hydrophobicity is not deteriorated, a hydrophobic material layer
may contain a catalyst for an air electrode for preventing flooding
and also improving activity of an electrode reaction.
[0044] Catalysts may be a platinum-ruthenium (Pt--Ru) alloy
catalyst in the fuel electrode side and a platinum (Pt) catalyst
supported by Ketjen Black in the air electrode side. To a catalyst
is added a hydrophilic polymer material solution such as a
Nafion.RTM. solution and the mixture is stirred to provide a
catalyst paste. The hydrophilic polymer material can constitute a
hydrophilic material layer formed on the surface of the fuel
electrode side and may be suitably a polymer compound having an
ionic group such as a sulfonic acid group, for example a
perfluorocarbon polymer having an ionic group such as a sulfonic
acid group, typically a tetrafluoroethylene polymer having a
sulfonic acid group in its side chain.
[0045] Then, to the fuel electrode side opposite to the air
electrode side in the electrolyte membrane is applied a Pt--Ru
catalyst paste to form a hydrophilic material layer. Thus, even
when the porous membrane used itself has insufficient
hydrophilicity, an interface between the electrolyte membrane and
the fuel electrode can be made hydrophilic. Furthermore, since a
smooth coating surface can be provided, adhesiveness between the
electrolyte membrane and the fuel electrode can be improved.
Although a Pt--Ru catalyst paste is herein used, a hydrophilic
paste without a catalyst may be applied. As long as desired
hydrophilicity is not deteriorated, the hydrophilic material layer
preferably comprises a catalyst for a fuel electrode for improving
activity of electrode reaction as well as proton conductivity.
[0046] Next, to current collectors for the fuel electrode and the
air electrode are applied the Pt--Ru alloy catalyst paste and the
Pt catalyst paste, respectively to give a fuel electrode and an air
electrode.
[0047] An electrolyte membrane comprising the hydrophilic material
layer and the hydrophobic material layer is sandwiched by these
electrodes, and the product is heated under pressure for making the
electrolyte membrane and the catalyst electrodes stick together to
give an MEA.
[0048] The MEA obtained may be used according to a known technique
to form a unit cell where an aqueous methanol solution is fed to a
fuel electrode without pressure while air or oxygen is fed to an
air electrode under, for example, an atmospheric pressure, or a
combination of a plurality of such unit cells to give a direct type
fuel cell of this invention.
EXAMPLES
[0049] A process for manufacturing an MEA will be specifically
described with reference to examples.
Example 1
[0050] A porous membrane used was a hydrophilic PTFE porous
membrane with a thickness of 25 .mu.m.
[0051] An aqueous monomer solution as a raw material solution for a
proton conducting polymer was prepared by mixing 6 g of
acrylamide-tert-butylsul- fonic acid as a monomer, 0.02 g of
2,2'-azobis-(2-amidinopropane).bishydro- chloride as a radical
initiator and 5 g of water.
[0052] The porous membrane was immersed in the aqueous monomer
solution for 2 min to impregnate the micropores of the porous
membrane with the aqueous monomer solution. The membrane was
subjected to polymerization at 60.degree. C. for 2 hours and then
dried. Next, the membrane was immersed in warm water at 60.degree.
C. for washing to remove unpolymerized materials and
low-polymerization products. The above process of impregnation,
polymerization and washing was repeated twice.
[0053] To one side of the electrolyte membrane thus obtained was
applied a 60% PTFE dispersion such that a resulting film has a
thickness of 1 .mu.m from the outermost part, to form a hydrophobic
material layer in the air electrode side.
[0054] A platinum-ruthenium (Pt--Ru) alloy catalyst was prepared as
a catalyst for the fuel electrode side while a platinum (Pt)
catalyst supported by Ketjen Black was prepared as a catalyst for
the air electrode side. Each of the catalysts was mixed with an
equal amount of an alcohol solution of Nafion.RTM. to prepare a
catalyst paste.
[0055] Then, to the fuel electrode side opposite to the air
electrode side of the electrolyte membrane was applied the Pt--Ru
catalyst paste to a film thickness of 1 .mu.m, to form a
hydrophilic material layer.
[0056] Next, to current collectors for the fuel electrode and for
the air electrode were applied the Pt--Ru alloy catalyst paste and
the Pt catalyst paste, respectively, to give a fuel electrode and
an air electrode.
[0057] An electrolyte membrane comprising the hydrophilic material
layer and the hydrophobic material layer was sandwiched by these
electrodes, and the product was hot-pressed at 120.degree. C. and
8.5 MPa for 2 min for making the electrolyte membrane and the
electrodes stick together to form an MEA.
Example 2
[0058] An MEA was prepared as described in Example 1, except that a
hydrophilic material layer was not formed in the electrolyte
membrane.
Example 3
[0059] An MEA was prepared as described in Example 1, except that a
hydrophobic material layer was not formed in the electrolyte
membrane.
Conventional Example
[0060] An MEA was prepared as described in Example 1, except that
hydrophobic and hydrophilic material layers were not formed in the
electrolyte membrane. This corresponds to the conventional example
in FIG. 2.
[0061] Each of the MEAs in Examples 1 to 3 and Conventional Example
was used to make a unit cell configured that a 10 vol % aqueous
methanol solution was fed to a fuel electrode without pressure and
air was in contact with an air electrode under an atmospheric
pressure. Its electric properties were evaluated by determining
output values at 25.degree. C. and 5.degree. C. and a discharge
time. The results are shown in Table 1.
1 TABLE 1 Maximum output at Maximum output at Discharge time
25.degree. C. (mW/cm.sup.2) 5.degree. C. (mW/cm.sup.2) at 5.degree.
C. Example 1 28 12 .gtoreq.180 min Example 2 23 10 120 min Example
3 25 9 110 min Conventional 20 7 90 min Example
[0062] As seen from the measurement results of the maximum output
at 25.degree. C., the output of Example 1 was most improved because
of improvement in adhesiveness and hydrophobicity in the oxygen
electrode side and improvement in adhesiveness and hydrophilicity
in the fuel electrode side. The results also show that Examples 2
and 3 gave a higher output than Conventional Example because of
improvement in adhesiveness and hydrophobicity in the oxygen
electrode side and improvement in adhesiveness and hydrophilicity
in the fuel electrode side, respectively.
[0063] As seen from the measurement results at 5.degree. C., any of
Examples 1 to 3 exhibited good output and discharge properties. In
particular, Example 1 gave particularly improved output and
discharge properties. It was because in comparison with
Conventional Example, improved adhesiveness between the electrolyte
membrane and the electrodes resulted in an increased output and
increased catalyst activity, which led to a higher auto-oxidation
heating temperature of the catalyst so that water generated by the
fuel cell reaction was more easily vaporized and a less amount of
water penetrated from the electrolyte membrane, resulting in
prevention of flooding.
[0064] In the above examples, an acrylic monomer having a sulfonic
acid group was radical-polymerized in micropores in a porous
membrane to form a proton conducting polymer filling the micropores
in the porous membrane. Alternatively, an acrylic monomer having a
sulfonic acid group and another acrylic monomer may be
co-polymerized in micropores in a porous membrane to form a proton
conducting polymer filling the micropores in the porous
membrane.
[0065] Furthermore, an olefin such as ethylene having a sulfonic
acid group as a substituent may be polymerized in micropores in a
porous membrane to form a proton conducting polymer filling the
micropores in the porous membrane. Alternatively, an olefin such as
ethylene having a sulfonic acid group as a substituent and another
olefin may be co-polymerized in micropores in a porous membrane to
form a proton conducting polymer filling the micropores in the
porous membrane.
* * * * *